amp in 08 mustang, car's dead

So, After years of doing my own, I figured id let someome else do my amp/sub isntall on my new 08 Stang gt. Directed 600d and mtx 7500 using my shaker 500 stock system. Get to car today, its dead. Try to jump, nothing. Then I go back to amp, lights on even when ignition is off. Pull the amp turn on lead thats tapped to ignition wire at steering column, still on....pull the amp fuse at battery, give the car a jump, starts... wth, can anyone point me in the right direction...why would the amp stay on - or maybe the light was slowly dimming (amp ON light) but im sorta at a loss. The shop is like, its probably your amp....ummmm Ive used that amp in 3 cars and its flawless....not the amp....unless this killed it which im sure they wont take responsibility for... Ideas...taking car back in an hour and wish I had something on them.....anyone ???

If you removed the turn on wire from the amp and it is still lit up, it is probably the amp.

Is there something the installer COULD have done at the time of the install to screw up the amp - IE wire to a higher current lead or something because that amp was working a week ago when I pulled it from my other car.. So annoyed if I have to buy a new amp and didnt need one - I love the DEI 600 too! UGGGG What could it be, why suddenly....

UPDATE - So I take it in, and be peeks in the car for 1/10th of a second and calls out "the amp is bad". I was so annoyed, I said you had to have wired the turn on wrong or something this amp worked fine a week ago. Then I though to myself...WHY WOULD THE AMP STAY ON...and it dawned on me...the power wire I bad a feeling was touching the turn on lead. So, I said to him - I bet 100 bucks, thats the prob, he was like no no no, and sure enough the power was in fact touching the turn on post....go figure. Coulda fixed it myself but in the end glad I could prove my point.... I guess if you want it done right, do it yourself :) All good....its workin! Thanks for posting/listening ;)